A communication system for next generation is designed to use frequency bands corresponding to broadbands and increase a data transmission rate between a transmitter and a receiver. For configuration of the communication system, OFDM based modulation is mainly adopted, and the wireless communication standard through the OFDM based modulation is applied to 3GPP LTE(+), 3GPP2 UMB(+), IEEE 802.16(d,e,m), IEEE 802.11, IEEE 802.20, IEEE 802.22, and HiperLAN. Examples of user classification modes include FDMA mode based on a frequency axis and a TDMA mode based on a time axis. In the communication standard configured to be used at low cast, such as wireless LAN and HyperLAN, CSMA corresponding to the TDMA mode is mainly used. On the other hand, in the system such as 3GPP LTE, 3GPP2 UMB, and IEEE 802.16, which supports commercial voice communication, traffics of respective user equipments are distinguished by FDM scheme to maximize frequency efficiency. Accordingly, the above systems allow data to be transmitted between a base station and a mobile station under the control of the base station, and information of the control is transferred to the mobile station through scheduling information.
In a communication procedure between a mobile station and a base station, scheduling for obtaining multi-user diversity is mainly used to maximize frequency efficiency. In other words, frequency resources are allocated in such a manner that a specific mobile station can obtain maximum throughput using minimum frequency resources. The scheduling result according to the above allocation is set to be decoded by the mobile station without error and then transferred. However, if channel status of the mobile station is not good, packet transmission between the base station and the mobile station does not end only one time but is accompanied with retransmission. Time-diversity and transmission energy boosting effects can simultaneously be obtained by packet retransmission. Although maximum throughput that can be obtained is reduced, packet retransmission is properly performed to configure a reliable channel. A hybrid automatic repeat request (HARQ) mode is mainly used for initial transmission/retransmission of packets as above. Packets transmitted and received between the mobile station and the base station are encoded through a channel code. Various HARQ modes are generated in accordance with a method of converting packets in various formats. The simplest method is that all codewords are used for every packet transmission. In this case, a receiving side performs decoding using chase combining. This method is one of methods of simply performing retransmission. As another method, there is provided a method of transmitting codewords by splitting them. This method is used by an incremental redundancy (IR) scheme. If there is new code bit information in retransmitted packets, it means that additional information is received. If the existing bits are received, bit combining is used.
FIG. 1 illustrates a procedure of generating packets according to HARQ.
FIG. 1 illustrates that configuration of transmission packets may be varied whenever the packets are transmitted through HARQ. If chase combining is used, packets are equally configured whenever they are transmitted. However, if IR is used, configuration of packets may be varied whenever the packets are transmitted.
FIG. 2 illustrates a procedure of decoding transmission packets from a signal combined in a receiving side.
If packets of FIG. 1 are received, the receiving side sets a part of the packets which are not transmitted from the position of each codeword bit to reliability of 0 and performs decoding, i.e., soft decision decoding. Alternatively, the receiving side assumes the part of the packets which are not transmitted as erasure and then performs decoding, i.e., hard decision decoding.
Also, in case of codeword bits transmitted in a multi-mode, the transmitted bits are used by combination. In this case, the bits may be combined with one another in accordance with soft decision or hard decision. When the bits are combined with one another in accordance with soft decision, it is assumed that channel correction has been performed. Then, the receiving side combines the receiving signals with one another and averages them through analog type or multi-bit precision. In this case, weighted combining can be performed in accordance with accuracy of the received bits. On the other hand, if only bits of 0 and 1 are required like hard decision decoding, 0 and 1 are selected based on majority when the respective bits are combined with one another.
Equation 1 represents soft combination when soft decoding is performed, and Equation 2 represents multi-selection when hard decoding is performed. The actual configuration of each of Equations 1 and 2 may be varied depending on a decoding method.
                              R          ⁡                      (            k            )                          =                              ∑                          i              =              1                                      N              R                                ⁢                                          ⁢                                    w              ⁡                              (                                  k                  ,                  i                                )                                      ⁢                          r              ⁡                              (                                  k                  ,                  i                                )                                                                        [                  Equation          ⁢                                          ⁢          1                ]                                          R          ⁡                      (            k            )                          =                  {                                                                      1                  ,                                                                                                                        ∑                                              j                        =                        1                                                                    N                        R                                                              ⁢                                                                                  ⁢                                                                  w                        ⁡                                                  (                                                      k                            ,                            i                                                    )                                                                    ⁢                                              r                        ⁡                                                  (                                                      k                            ,                            i                                                    )                                                                                                      >                                                            N                      R                                        2                                                                                                                        0                  ,                                                            Otherwise                                                                        [                  Equation          ⁢                                          ⁢          2                ]            
In this case, R(k) means soft/hard decision information of the received bits, r(k,i) means soft/hard value in the ith HARQ packet reception, and w(k,i) means a weight value to be applied to a corresponding bit in each transmission packet when combining is performed.
The aforementioned transmission/decoding method is suitable for a general blind channel. Also, the channel can have optimal throughput in a state that all bits have the same uncertainty as one another, like AWGN.
However, in the packet transmission and retransmission method according to the related art, throughput may be varied depending on channel/transmission type to which the aforementioned decoding method is applied.